public inbox for gcc-bugs@sourceware.org
help / color / mirror / Atom feed
From: "segher at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug target/68837] PowerPC switch statement performance
Date: Thu, 04 Jun 2020 20:18:20 +0000	[thread overview]
Message-ID: <bug-68837-4-ESEwmdZrpR@http.gcc.gnu.org/bugzilla/> (raw)
In-Reply-To: <bug-68837-4@http.gcc.gnu.org/bugzilla/>

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=68837

--- Comment #4 from Segher Boessenkool <segher at gcc dot gnu.org> ---
On Power9 the lwa insn is cracked into an lwz and an extsw, just like
on older CPUs.  Cracked instructions have fewer constraints on p9 than
they did on most older CPUs though (it doesn't have to be first in a
fetch group any more).

It still saves one insn to execute if lwz would be enough.  Another
option may be to just do an ld even: this saves the number of insns
needed, but it takes more space for the table (so it won't be cached /
prefetched as well), and absolute addresses require relocations.

  parent reply	other threads:[~2020-06-04 20:18 UTC|newest]

Thread overview: 4+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
     [not found] <bug-68837-4@http.gcc.gnu.org/bugzilla/>
2020-06-03  9:08 ` guihaoc at gcc dot gnu.org
2020-06-04 15:43 ` dje at gcc dot gnu.org
2020-06-04 20:18 ` segher at gcc dot gnu.org [this message]
2020-06-11  5:15 ` guihaoc at gcc dot gnu.org

Reply instructions:

You may reply publicly to this message via plain-text email
using any one of the following methods:

* Save the following mbox file, import it into your mail client,
  and reply-to-all from there: mbox

  Avoid top-posting and favor interleaved quoting:
  https://en.wikipedia.org/wiki/Posting_style#Interleaved_style

* Reply using the --to, --cc, and --in-reply-to
  switches of git-send-email(1):

  git send-email \
    --in-reply-to=bug-68837-4-ESEwmdZrpR@http.gcc.gnu.org/bugzilla/ \
    --to=gcc-bugzilla@gcc.gnu.org \
    --cc=gcc-bugs@gcc.gnu.org \
    /path/to/YOUR_REPLY

  https://kernel.org/pub/software/scm/git/docs/git-send-email.html

* If your mail client supports setting the In-Reply-To header
  via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line before the message body. 
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for read-only IMAP folder(s) and NNTP newsgroup(s).